1. Field of the Invention
The invention relates to an apparatus for the bilateral blowing of a treatment gas onto a web-like or sheet-like material comprising a treatment space for the approximately rectilinearly moved web-like or sheet-like material, nozzle ribs arranged on both sides of such material for introducing the treatment stream into the treatment space and radial fans on the one hand for generating the treatment stream supplied to the nozzle ribs from one side and on the other hand for extracting the treatment gas from the treatment space on the opposite side.
2. Description of the Prior Art
Such apparatuses are used in the heat treatment of material webs or sheets, such as of textiles or metal sheets, plates or strips of glass and other similar products, for the purpose of heat exchange and also for drying purposes. Hereinafter the term web-like material covers both endless webs and sheets of material and the term material web also covers material sheets. To ensure as uniform as possible a blowing onto the surface of the web-like material nozzle ribs having nozzle openings are provided transversely of the transport direction of the web.
The gap between two adjacent nozzle ribs is available as flow-off cross-section for the treatment gas flow blown with the nozzles onto the web or sheet, the web usually being guided horizontally. The guiding, for example in the case of light strips, may be contactless by means of floating nozzles; in particular in the case of heavy web-like materials, rollers are arranged between the nozzle ribs of the lower nozzle field, said rollers supporting the web-like material and, in the case of driven rollers, simultaneously conveying said material.
In particular in the case of relatively wide web-like or strip-like materials a uniform convective influencing with the treatment gas stream is ensured only if the flowing back of the treatment gas stream takes place completely uniformly on both sides of the web, i.e. upwardly and downwardly. In the article "Apparatuses for the heat treatment of contactlessly guided sheet metal strips" by Kramer, Stein and Gerardt, published in "BANDER BLECHE ROHRE", Nov. 1975, p. 453 et seq., it is proposed for this purpose to provide fans above and below the web plane, the flow path for the upper and lower half of the apparatus thereby being symmetrical with respect to the lay. However, the serious disadvantage arises here that the fans serving as flow drive for the treatment gas stream acting on the web from below cannot be installed in the space still available beneath the nozzle ribs down to the floor. To maintain the working height of about 1 m to 1.5 m usual for material webs it is therefore necessary to provide beneath such an apparatus a pit which is so dimensioned that dismantling of the fans arranged beneath the material web is possible and in addition enough room is available for inspection and maintenance work. Consequently, such a pit involves a high technical and economic expenditure for the installation of a constructional form of this type.
German Pat. No. 2,446,983 further discloses an apparatus for bilateral blowing of a treatment gas onto a web-like material in which nozzle ribs arranged on both sides of the web-like material are provided for the introduction of the treatment stream into the treatment space and a fan is provided on the one hand on one side of the nozzle ribs substantially in the centre of the treatment space and has a horizontal axis for generating the treatment gas stream supplied to the nozzle ribs from one side and on the other hand a fan is provided on the opposite side for symmetrical extraction of the treatment gas. Since the radial fans for driving the stream are arranged laterally of the material web even with relatively large web widths no pit is necessary beneath the apparatus. Moreover, the flow guide above and beneath the plane of the material web is completely symmetrical and is therefore particularly suitable for the floating guiding of material webs, i.e. for example as floating furnace or floating drier for strips.
However, if in such an apparatus the material web has to be led over rollers as is necessary for example in the heat treatment of glass sheets, due to the arrangement of the radial fan with its discharge housing on one side of the material web there are restrictions on passing the rollers transversely through the apparatus and the location on the fan side and this is moreover very difficult.
Furthermore, the rollers must be substantially longer than the web width. This is another serious disadvantage in particular in apparatuses which have to be operated at relatively high temperatures.
A similar apparatus is disclosed in German published specification 2,056,190 where a radial fan is incorporated in a 360.degree. spiral housing and blows into a single discharge duct of constant cross-section.
Such a housing is suitable only if considerable losses in efficiency are accepted for fans with a high reaction degree in which the pressure development takes place substantially in the impeller. In fans with radially terminating or forwardly curved blades and in particular with drum impeller fans such a housing is completely unsuitable. Moreover, the apparatus according to the published specification has only a single fan on each side of the material web supplying simultaneously the nozzle arms arranged above and below the material web. As a result, with such an apparatus the nozzle pressure of the upper nozzle arms cannot be varied with respect to the nozzle pressure of the lower nozzle arms.
Finally, this apparatus is intended for blowing treatment of textile webs of fibres, for example chemical fibres, which as a rule are air-permeable. The ventilation conditions are therefore completely different than with air-impermeable materials and consequently a completely symmetrical flow path above and beneath the material web plane is practically impossible.
Finally, German specification as laid open to inspection 2,265,313 also discloses a continuous drier for webbed materials having only one air conveyer, the air guiding of which is first linear, then upwardly offset 90.degree., then 90.degree. laterally offset and finally merges offset 90.degree. in a further air supply conduit. This extremely unfavourable flow guide makes any setting of defined flow conditions impossible.